The season of good cheer might be the time of aging faster, according to a new way of looking at the risks of drinking, smoking, and overeating.

Action Points

A better way to communicate the impact of a lifestyle or environmental risk factor to the public may be the concept of a "microlife," defined as 30 minutes of life expectancy, researchers suggested.

Note that people lose a microlife for every two cigarettes they smoke, for being 11 pounds overweight, for having a second or third alcoholic drink of the day, and for eating an extra portion of red meat daily.

The season of good cheer might be the time of aging faster, according to a new way of looking at the risks of drinking, smoking, and overeating.

People lose a microlife, or half-an-hour of life expectancy, for every two cigarettes they smoke, wrote David Spiegelhalter, PhD, in the Christmas issue of BMJ. Being 11 pounds overweight, having a second or third alcoholic drink of the day, and tucking into a burger each also cost a microlife, he added.

The usual ways of expressing the risk of such behavior -- hazard ratios, standardized mortality ratios, and population attributable fractions -- often don't strike a chord among lay people, argued Spiegelhalter, who is Winton professor for the public understanding of risk at the University of Cambridge in the UK.

To make matters plainer, Spiegelhalter suggests converting hazard ratios into "microlives," defined as 30 minutes of life expectancy. Losing microlives is equivalent to aging faster, he said.

"Smoking 20 cigarettes a day (10 microlives) is as if you are rushing towards your death at 29 hours a day instead of 24," he wrote.

On the other hand, people can gain a microlife by exercising for 20 minutes, taking a statin, stopping at one drink a day, or eating fresh fruits and vegetables.

Spiegelhalter computed a million half hours -- or 57 years -- roughly corresponds to a lifetime of adult exposure to any given hazard. Indeed, he noted, at current mortality rates in the UK, a 35-year-old can expect to live another 55 years or 481,000 hours or very nearly a million microlives.

The approach "allows a general, non-academic audience to make rough but fair comparisons between the sizes of chronic risks, and is based on a metaphor of 'speed of ageing,'" Spiegelhalter wrote.

As an example, he cited a recent study that suggested eating an extra portion of 3 ounces of red meat daily was associated with a hazard ratio for all-cause mortality of 1.13.

If that's converted to a change in life expectancy in Britain, he said, a 35-year-old man with a lifetime habit of that extra few mouthful of red meat a day is looking at living to 79 instead of 80.

"This does not look very impressive, as people tend to dismiss effects that are perceived to lie in the distant future," Spiegelhalter commented.

But the loss of 1 year over 45 works out to about half an hour a day, so that a burger a day over a lifetime is associated with losing half an hour a day in life expectancy, he said, "which is, unless you are a quite a slow eater, longer than it takes to eat the burger."

Spiegelhalter also noted that demographic factors -- not just behavior -- can be expressed in microlives. Being female rather than male is equivalent to a gain of 4 microlives a day, while being Swedish rather than Russian gains 21 microlives a day for men.

The approach has some limitations, Spiegelhalter noted. It ignores variability among people and does not apply to specific ages or single exposures. Also, microlives reflect epidemiological differences among groups, and don't necessarily express causal effects of the various behaviors.

There is also no consideration of quality of life, he noted, "so behavior is evaluated only in terms of adding years to life, rather than life to years."

One possible effect of the analysis might be that people would think of trading off microlives -- 20 minutes of exercise this morning, for instance, against an extra glass of wine at dinner.

Indeed. there is some evidence that such trade-offs "may not always be unreasonable," Spiegelhalter noted. One major study found that four risk factors for mortality -- smoking, alcohol consumption, physical activity, and diet -- - were actually independent, he noted.

Whether communication risks in terms of microlives would have any effect on behavior remains uncertain and will need study, Spiegelhalter noted.

"But one does not need a study to conclude that people do not generally like the idea of getting older faster," he concluded.

The journal said Spiegelhalter reported no external support and that he had no potential conflicts.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco

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